1. Field of The Invention
The present invention relates generally to a vane type fluid pump. Specifically, the present invention relates to a variable fluid volume vane type pump which may be utilized in automotive engines.
2. Description of The Prior Art
Vane type rotary pumps capable of variable fluid volume operation are well known in the automotive field. For example, Japanese Patent Application First Publication (unexamined) 62-276286 discloses one such conventional variable fluid volume vane pump for automotive applications.
According to the above arrangement, a housing, a cam ring and a rotor provided with a plurality of radially arranged vanes is provided. An inner circumferential surface of the cam ring is circular and is contacted by the vanes according to rotation of the rotor. The housing is provided with fluid inlet and outlet containments and fluid is moved from the fluid inlet to the fluid outlet according to movement of the vanes.
Also, according to the above-mentioned disclosure, semicircular grooves are provided respectively oil both sides of the cam ring for communicating between the inlet and outlet containments provided at the inner circumference of the cam ring. According to this construction, a width of the grooves is kept smaller than a thickness of the vanes attached to the rotor.
As mentioned above, communication between the inlet and outlet spaces is dependent on the grooves, thus the grooves mitigate pressure variation based on eccentric load etc. applied to the pump so as to prevent cavitation and reduce pump noise.
According to normal operation at a constant pump speed, the above measures are sufficient for suppressing cavitation and reducing pump noise. However, when an operating speed of the pump is subject to variation or fluctuation, such that pressures at the inlet and outlet containments are increased while pump timing is varied, is is extremely difficult to cancel out such pressure variation to prevent cavitation and pump noise.